This invention relates generally to clay and clay minerals, i.e. to crystalline 2-dimensional layered lattice silicates having the general formula E.sub.i M.sub.x Si.sub.y O.sub.n (OH).sub.m, where M is Al, Mg, or Fe; x=2 to 6; y=2 to 8, n=2 to 20, m=0 to 8, and E.sub.i is one or more exchangeable ions (K, Na, Mg, Ca, Ba, Fe, Li, etc.). These layered silicates will hereinafter be referred to in this specification as "layered lattice silicates". More specifically, the invention relates to a method for aminating materials of this type, including e.g. kaolins and kaolinitic minerals, in order to produce products having new and unusual properties rendering same useful for a variety of purposes, including especially as fillers in plastic, rubber and other systems. The said products can also be more generally regarded as intermediates for subsequent functionalization thereof.
In the instance of clays such as kaolin clays, it has long been recognized that products having new properties and uses can be formulated by combining these aluminosilicates with organic materials. However, useful progress in this direction has tended to be limited by the lack of available covalent bonding at the mineral/organic interface. In the past this difficulty has been partially overcome by surface modification of the kaolinite through coupling of organo-silane compounds and subsequent reaction between dependent silanes and organics.
Thus, in Papalos, U.S. Pat. No. 3,227,675, for example, kaolin clays are described, the surfaces of which are modified with organofunctional silanes. A typical such agent e.g. is a methacryloxypropyltrimethoxy silane. The kaolin clays so modified are advantageously used as fillers for natural and synthetic rubbers and the like. It is also pointed out in this patent that such modified products can serve as intermediates for synthesis of new pigments, which are useful as fillers for polymers, elastomers and resins. This result obtains because the silanes used to modify the kaolin clays are di- or polyfunctional, and only one functional group, the silane, is attached to the clay, leaving the remaining reactive groups to react further.
Additional references of this type include Iannicelli U.S. Pat. No. 3,290,165, and Iannicelli, U.S. Pat. No. 3,567,680.
However, the modification of aluminosilicates such as kaolin clays by the use of organosilanes, is a complicated and expensive process. Among other things, the cost of the organosilane itself is very high. Furthermore, the resulting products have only limited capability for further functionalization, regardless of the particular organosilanes utilized.
In a 1979 article by the Soviet authors Savchits, Romanovskii, and Egiazrov, entitled "High Temperature Amination of the Surface of Oxide Catalysts", it is reported that the surface hydroxyl groups of high surface area aluminosilicate catalysts can be replaced by surface-bound NH.sub.2 groups via a high temperature gas stage reaction with ammonia. This reference is concerned with examining those conditions under which ammonia does not modify the surface of the catalysts, and has no applicability to low surface area, 2-dimensional layered crystalline, naturally occurring mineral materials, such as the clay materials which are of primary interest to the present invention.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a relatively simple, inexpensive, and effective process, which enables surface modification of a clay mineral, such as a kaolin clay, by surface-bound NH.sub.2 groups, thereby providing a new product having valuable applications, e.g. as a filler for paints, plastics, rubbers and paper.
It is a yet further object of the present invention, to provide a novel process for preparing analogs of known silanemodified silicates, such as analogs of known silane modified kaolin clays and the like.
It is a yet further object of the present invention, to provide a process and products, which enable the production of filled systems, for example, resin-filled systems, incorporating the products of the invention, which have superior properties with respect to mechanical aspects of same, as compared to prior art filled systems based upon prior art kaolin clay, and similar fillers.